Before Pressing Cycle Start

Always verify the following before running any program:

Are you running the right program?
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If you can't confidently answer "yes," go back and check. Accidentally running the wrong program with the wrong setup could cause a serious crash.

Did you install the right tool?
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Many tools are alike. Always double check that tool number matches what the program asks for.

Is your workpiece secure?
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If it can wiggle it free, don't machine it.

Did you close the machine doors?
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This is what stands between you and a hungry spindle that flings sharp chips (and in the event of a crash, parts) in your direction.

Are you ready to press the Emergency Stop button?
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Also, did you read The Emergency Stop Button? If you haven't, go do that first.